Temperatures along the coast and in the western valleys will be somewhat cooler, but still 5 to 10 degrees above average, according to the weather service.
The heat wave will kick off Friday, with the mercury climbing into the upper 80s in San Jose and into the mid 90s in Morgan Hill, Pi said.
An excessive heat warning will be in force in the San Gabriel Mountains from 11 a.m. Saturday to 9 p.m. Wednesday, in the Antelope Valley from 11 a.m. Sunday to 9 p.m. Wednesday, and in the Santa Clarita Valley from Monday morning through Wednesday night. Pi encouraged Bay Area residents to drink plenty of water and to stay out of the heat as much as possible.
The Phoenix forecast office says all-time high temperature records could fall. In Southern California, the hottest temperatures will be in the deserts with highs over 110 degrees.
Hikers and others planning to go outdoors are advised to stay in groups, keep hydrated, dress for the heat in light and breathable clothing, take regular breaks and stay indoors if the heat becomes overwhelming.
Nighttime temperatures are expected to be around 60 degrees.
He added it was critically important to never leave children, elderly people, or pets unattended in homes without air conditioning and particularly in vehicles, even if the windows are "cracked" or open, as temperatures inside can quickly rise to life-threatening levels.
Heat indices are expected to reach the triple digits Friday and Saturday despite isolated thunderstorm predictions and an incoming cold front.
"Probably daily records, which are about 115 to 118 each day and then also the fact that we will be above 118 for four days in a row, that would also set a record", said Hirsh.
In California, triple-digit heat will engulf Bakersfield, Fresno and Sacramento starting this weekend and continuing into next week.